Mounting for tracers



Dec. 6, 1949 P. M. HENKES ET AL 2,490,128

MOUNTING FOR TRACERS Filed Feb. 8, 1945 4 Sheets-Sheet 1 INVENTOR. PETE/E m yaw/5 FEED JYZ'IA/B/E'd/fik A TTOENEM P. M. HENKES ET AL MOUNTING FOR TRACERS Dec. 6, 1949 4 Sheets-Sheet 2 Filed Feb. s, 1945 Dec. 6, 1949 P. M. HENKES ET AL 2,490,128

MOUNTING FOR TRACERS I 4 Sheets-Sheet 3 Filed Feb. 8, 1945 A BWMMJ Dec. 6, 1949 P. M. HEN-KES ET AL 2,490,128

I MOUNTING FOR TRACERS Filed Feb. 8, 1945 4 Sheets-Sheet 4 V M n l "5' ii. l lmn L x I UNITED 1 r n V This. iinyention- .rela-te" to improvements in hothz thesiwonkeendzthemaittem ea thenwarere Patented Dec. 6, 1949 MGUNTI-NG FORTRAGERS @BetenMeHenkes and: Fred. SQt embreckereRaeiuer, V .Wis., assig nors to Geor'ge.Gorton.Ma el1ine Cm}!!! ;pany,-.Racine, Wis .v a con'poi-atioii'of Wisboiisln Appiiattiii Fbbi'ddi' y8, 19455;"SQEHFNUFS'ZGE'IQ'GJ 8-, Clai ms; ((31.490-13). I

El -s roF-rromountings for tracers forming a; part or control systems-for: machine tools.

Threerdimensionalzx-controlatracers, whichi are if used with, machinetools-:ofr-thezsot-called duplica' tor type; m'ust be movable-longitudinally with-the cutter spindles. :It has-been the practice to mount rtheitracersz om 'spindlesttslidablyi carried at therendsofrigid' arms' 'projeoting laterally"from I the cutter'heiads of tl'ieimachines. -:Such spindles are:moved:simultaneouslywith: the cutter: spindle by means "of gear teeth in1=the;- quills;.orcutter spindle sleeve mesheduwith pinions- 'o'n azrcross shaft carriedinsuchFrigidsarmS. O/neoftheide fectsoil-this" constrhctioni iss-thef transmission of detrimental vibration-etc the tracer by such arms; Another. objection: is1=the= loss :of ;.'a-ccura'cy and: the undesirable lag bet-weemtraeer 'spindleeandcutter spindle resulting from -the use-rot: shafting "and gears-toefiect simultaneousmovement;

One of the objects ofsthepresentr invention therefore is to providers. mounting-for. tracers which will. nottransmit'sharmful vibrations to the tracer.

Another object of; the invention is to provide a mounting for the --tracer which willy cause the tracer to move simultaneously with the cutter spindle without -any= measurable. lagtherebetween.

The .foregoing .o'bjects are obtained: by providing-a main supportingsarm-aud vfixed guiding member rigidly securedz-to ther-cutter head; by providing a relatively-movable member which-is guided by, the fixed guidingmember to reciprocal movement parallel. to, the longitudinal. movement. of, the cutter spindle; by' balancing. the, control arm and tracer-carrying farm with the tracer about" the relatively movable member; by provid-, ing a frictionles's sliding "beai'ing between the.

tween the fixedguide: and the relatively movablememberv preferably hasrconsiderable length to prevent-any movement therebetween other than in-a'fixedaxis'parallel to=the=axis of the :cutter spindle. -By .balancing;-the;controlarm and trace-- er-carrying arm about -the relatively movable memben, unnecessarynvibrations are eliminated,

andsstill thetracer meyrbescarried at a. sufficient distance from the cutter spindle to accommodate 'end toeend relationship. Thecdirecticonnectioh between tne relatively movable member -ar'id time qu'illnof the-butter spindle eliminatesilagF-and relative 1 movement." therebetween, rand It-hus laconrately moves theastylusfcarried by the ztracer stmultaneously:--.with.=theaaxial movement of the cutter. V

Referringtto.thewacoompanyingdrawings formingga-ipartihereoti ligure 1': isiawiewinperspective; of a three-dimensional trac'ersmouiiting em bodying the invention', zsuch mounting "beingf'ait tachedtothecutter headaofe verticali'millingtmap chine shown only in fragmentary view;

'15 -i'Figure-2km;topplamViewohtheztracer mountingiof -Figurerl withodiacent portionsoftthe. mill; mg. machinevshown; diagrammatically;

is a-i.fragmentaryxsectionalview taken om the; line? 3 3mflFigureQlto;illustrate thee-slid:-

inggbearing;betweens'theifixed guide andithearela tively movablemember;

:Rigu-re 4 -45 avfragmentarmsectional view; taken on the linevl-4l.of*l fizurel3 Figure-Mean enlarged: sectionala view taken-:01:

V Figure 6.11s an enlarged sectional vievmtaken'ion the line 6--6 of: Figure? 2';

Figure -'l -is: a. fragmentary enlarged :"sectional view taken. on the-lineflr-'li ofFigure-2;

E g-ure;s:ls;.-a;perspective-view of the;main-:sup-

porting arm or'flxedguidingimember andithecorntrol arm which 'connectsithe, relatively movable member tethering, om-thet-quill of'the cutterespindle; and

iFig ure-i 9 is a. perspectivewiew of a. modifiedformof tracer mounting.

:Referringl in greater. detail to the drawings, the mountingionthetracer is shown'"on;--a.-vertical' milling-machinerdesignated generally'zat I10. The

40 machine i0: is :shown only} impart. 'TaSv s v a design. known 470i those r-skilled in thewart. -'It a rant H "which carries--21 tcutter:head I'Z inr-whicll:

is mounted the cuttertspindle t3; earriedin a uill or sleeve i311" whichjprovides for its 7. reciprocal longitudinal-movement. tAE-lug-M carried by the:

quill projectsa-zoutwerdlw from. the; cutter headsv througha slot. This:iug1-customarilyf0rms:one of-ithe: elements "of the-adjustable spindle-z depth. stop mechanism,illustrated-generallyat i5. In. this instanceit is also usedwith: the tracerrmounts ing; ashereinatter described;

:Thetraoer l-6,;showmin-Figure- 1, is of the-three! dimensional---type=, and: is. ifullyv described vandelain'iedw-inlen application ,Srial No.; 5.4'.7-;08l-, of;

Theodore Miller filed July 28, 1944, and now pending in the United States Patent Office, and assigned to the same assignee as this application, which application is entitled Tracers. The tracer I6 is mounted by a coupling flange 96 to the micrometer universal adjustable tracer-holding mechanism 6| hereinafter more particularly described. The operation of the tracer IS in the control of the movements of the table and in the vertical feed of thejcutting spindle are fully described in the foregoing application and in another application, Serial No. 514,125, of Theodore Miller filed December 13, 1943, and now Patent No. 2,247,201, granted August 17, 1948, assigned to the assignee of this application and entitled "Tracers and tracer controlled operation of mathe purposes of this invention, it is pointed out that the tracer in order to operate accurately and to be sensitive must remain in a fixed position relative to the cutter spindle in all positions of the latter. It must move along a fixed axis parallel-to the axis of rotation "of the cutter spindle in thesame direction and in the same amounts and at the same time as the movement of the cutter spindle along such axis of rotation. To acchine tools and other cutting machines. For

complish this, there is provideda main support or arm I! which is rigidly secured to the cutter head l2 by having its base portion I8 bolted or otherwise fastened to the side of the ram. The arm IT projects laterally from the ram, and its outer end is provided with an elongated casing l9, which provides a housing for the balancing spring 50 and a support for the fixed guiding member ofthe ball bearing slide hereinafter described.

The tracer support designated may be constructed of two parts. Onepart may be designated the control arm 2|. It has at one end an elongated casing 22 which is positioned opposite the casing l9 and forms the support for the relatively movable member of the ball bearing slide. The casing 22 is provided on its outer ends with two mounting pads 23 and 24 (see Figure 8) on which the detachable tracer-holding arm 25 may be alternately mounted. The other end of the control 'arm 2| has a jaw-like portion 26 which straddles the lug l4. Each of the jaw members has an adjusting screw 21 which engage the lug M from opposite sides, and by means thereof motion imparted to the lug II by generally at 20 g 2| to cause the tracer to the movement of the quill will be simultaneously imparted to the tracer control arm 2| without any lag or relative motion therebetween. j

The ball bearing slide or guide between the. main support I! and the tracer support 20 com prises a pair of opposed outer ways 28 and 291 (see Figures 3 and 4) whichare bolted to the face of the casing l9 and form a fixed member. The opposed faces of these ways are grooved to receive a plurality of spaced balls 30. A pair of into one side of the casing IS. The adjusting of these screws moves the way 29 inwardly toward the way 28, thereby placing the balls and ways under desired compression. End plates 40 and H are provided on the top and bottom ends of the ways 28 and 29, and end plates 42 are provided on the tops and bottoms of ways 3| and 32 to prevent the balls and their respective retainers from leaving the waysas'such ways are moved relative to each other. These plates have overlapping projections which cooperate to cover the end of the grooves in the ways and still permit relative movement between these plates. It is desirable to proportion the length of the retainers that when the inner ways move from one extreme to the other extreme of their travel relative to the outer ways, the rolling action of the balls will not be hindered by the retainers striking at either end of their travel. The ball bearing slide is relatively long and thus prevents canting and resultant binding between the movable member and the fixed member as they move from their extremes of travel.

In order to lessen the strain 'on the lug l4 and to increase the sensitiveness of the entire device, the total weight of the movable member, the control arm, the tracer-carrying arm, and the tracer is substantially completely carried by a coiled compression spring shown in detail in Figure 7. The lower end of spring 50 abuts on a bearing 5i carried on the bottom of the casing IS. The other end of spring 50 abuts against an arm 52 secured to the inner face of casing 22 and projecting within the casing 19. To prevent the spring from buckling as it is compressed, a tube 53 is inserted within the spring and is mounted on a pad carried by the arm 52. The tube 53 is slidably guided in an opening in the bearing 5|. Thusly balanced, it requires only a nominal force transmitted from the lug Hi to the control arm move simultaneously with the cutter spindle.

The tracer-carrying arm 25 has an enlarged end 60' provided with a flat surface engageable with either of the mounting pads 23 or 24. This end is flatly positioned on the desired mounting pad, and thereafter bolted or otherwise rigidly but detachably secured. The outer end of the arm 25 carries a micrometer adjustment mechanism shown in Figures 5 and 6 by means of which the tracer may be adjusted universally to a desired position relative to the cutter spindle. This adjusting mechanism will be hereinafter described in more detail. It is a 55 feature of this invention that the control arm 2| inner ways 3| and 32 are bolted to the inner face of casing 22 to form a relatively movable member. These ways also have ball bearing-receiving grooves oppositely related to the groovesin the ways 28 and 29. In order to obtain a proper] rolling action, the balls 30 are kept in properspaced relationship during the relative movement of the members of theguide, by retainers 33 and 34 which have holes for each ball. These retainers are positioned, and are freely slidable,between the opposed faces of the ways and move to permit the rolling of the balls. In order to permit adjustment of the ball bearing slide, a pair of adjusting screws 35 (only the'upper one of which is shown in the drawing) are threaded and holding arm 25 are proportioned so that the center of gravity of the entire movable part, in-v cluding the tracer, is substantially centered about the sliding bearing. This permits the tracer to be spaced a greater distance from the cutter spindle than if the weight of the tracer were supported by an arm extending from the main frame or cutter head of the milling machine to thetracer. Detrimental vibrations are prevented by thus supporting the tracer. With the carrying arm 25 positioned as illustrated in Figure 1, the pattern is placed in substantially end-to-end rela tion with the work. If it is desirable because of the unusual length of the work to place the pattern and the work in side-by-side position on the table, the carrying arm 25 is positioned on the pad 23 and extends at to the control arm 2|,

thus placing the tracer l6 outwardly of the cutter spindle. However, the pads 23 and 24 may be;

pI-acedwat othenrelativesangieszthanzllt'i?ito azcoma plish azdesired'nffesettingrtofithe:tmacer i5;-

The universal microsadjustmentfhol'dingt'meche anism; designated; generally: atfiifill, is shown =5 in detail in Figures 5 l "and -1 6. micrometer 'vertical;adjustment by means riot a tube 62 :slidabl-y vcarr-ied in a "circular -.:opening. formed" in :the:: outer: end; Tofu thew-ltraoereholding arm 25. The tube" has: a longitudinal::slot'ifiiilito accommodate :the projection: :of :thee: fixed:- nuts holding member."-6'4-; This memherlfits i-loosely in :a slot -formed in :=theacircula1topeningzzlfacing: the :end or? thearm i2 5-- andzislheidzfixedlwinzplace; against=one side of ,the slot iibyzdowel pins::.:=65 andlscrewsw fifia :A threadedsshaft 1 61:15;- rotatably mounted in the tube 62:and: is threadedly:fitted within. the fixed nut; on :theimember fi li-z-sorthat rotation of B the shaft by means? of 4a; hand wheel 68 will cause the screw-to; travelslongitudinally up. and down. through the: nut. 4A1 thrust-bearing: 69: acting on a .cap 1-G:-which-.is,secured: to l-the up per. end i of the tube. 62 vcauses the tube -to move. longitudinally vwith the shaft "6]. A micrometer: dial?! is adjustably carried omthelhubiof the hand wheel' 68: and is'-v marked-with indications to show the longitudinal movement-of-the tube-62 resulting from the rotation of the hand wheels-68. It .is important that the tube 6'2-be, prevented fromt. having. any. rotational ,movernent when it is adjusted longitudinally. To prevent such movement, the .tubelis provided with two -longitudinally extendinggrooves 12. which areplaced. on. opposite sides of. and,parallel the 4 slot 53. A. pair of screws 1 3 provided with locking nuts. are. threaded in ltheiend vof. the arms-in respective alinement with 'theslots '12. Iflhe endsxof the screws 13 lengage'the bottom and the-sides,of,the-. respective. grooves '12 to. prevent anyrotational movement of the tube 62. AclampinglscrewT113. provided with an operatingl'finger 'spansthe. slot formed in'the circular openingffacingathe outer end of the arm'zfi and'passesithroughthefixed nut-holding menr iber '64. When this screw is' tightened, the size of thelcircular Opening is decreased, "and it clamps 1 the tube '62 in place and prevents any movement 'therebetween after "the final adjustmenthas been obtained;

' The universal lateral adjustment of theyt'racer is" obtained" throughthe use of two slides; havin adjustments in planes arranged"90 apart: "This mechanism is well known "to'those skilledin'the' art and" will "be described only generally. "The top" slide designated generally at flvis'fsecured' to the tube" 52"by means of aJprojection flttingf'in the bottom thereof f and h'el'titherein' by a tapered pin. Rotation of? the "hand. wheel 8 I causeythe travel member- 82-" to have movemenfibackand forth in-one plane. Rotatiomofthe'iiandwlreel 83 causesa secondtravelingmemberfl'td have moveinentback' and forth ina plane perpen'dicular to that first mentioned. "Asdswll known; clamp screws areusedto lock the various traveling members when the proper"adjustment-has been reached. Thetracerproper hasits coupling flange 90' fastened by screws or "other "means' to" the travelling member 84. 'It'-will"be*se'en that the tracer may be adjusted by this-mechanism vertically and universally horizontally reiative tothe axis of rotation of the"cutter spiifdle-and hence the cutting tool carried thereby. 7 The' function of the micro universaladjustment is to "facilitate the final 'alinement" "of the stylus carried by the-tracer-with the pattern-after the' pattern and the work have b'een secured to the table of the milling l machine;

Iteprovides J for a" atiiustmenta 'hasidreewmqmphsnedz ithewdjust aiocke'dr-scnahat ithe "relative positiondietweeuathe tracersand E-thetcutting tool remainizflxediiflurixrgkeany 'mnvemeutreffithem as a: uniti;.reiative;=:tomie worhrand-epattem;

Tin:tneaemhodinrenttofitheiinventiom'heretofore describedilwhestraicen-1hasrbeenipositioneiiasat 1a substantial dlstanceafrmnathe -tsfdez:ofithe cutter spindle rim-writer toigpe'rmit bhEEWOIkLMd the L 'patternstozlbezpiaced'z'in end-itc-tendiapositiom'on lnv'suchsinstance thec'sconm'ol :amrmaymeelimi nate'dir entirelysziand the" 'slidingsgui'de? insteaid 'o'fz' being: amounted 'on az. main support extending laterally fromtthez cutter lheadrmay bemiounteddirectlyionv-tthesirontlbf"Ithezcutterdread; ,This

modification-sis shownxinw FigureQ wherein-Lthe outer-ways arezsecmted to:a:"flat=iface--96stormed on ithe zfrontrroffzthe 'zcutter 'iiea'd' i2. The :inner' waysrwhicli fl between thetouter waysesubstantially in razmanner identical rwithathataheretofore described? with: :respectuzto :the ways" 31:, are

mounted: 3011f a-m'ectangularly "shaped i'rhl'ock "-91 whichifhas n; outwardfzprojectionfito which :is

fastened: earnings-arm 98; iThe-i-armx flil i hasl its outwarkizaendwrovliied"with 'iasteningtmeans forl holdingrthe-ltracer eithersuirectiy orabyrmeans of: a micnouniversaliadjnstment mechanism simi-= lar to that heretofore described; snxlug inot shown": inith-e 'rlmwing) 1 similar to lug l 4': extends from the :cuttemspindle' quilhowsleevemnd directlyengagewwith *the travelling l-block 9! to cause: it to:move-ilongitudinally "with the cutter spindle- -withcutu any relative-movement therebetween. 'Azsiis fiwlli known :to th'ose skilled in thwartfltlle weightpfithecutter spindle isvsubstantiallyrtoarrierl ziwr a balanced: condition by a spring mounte'diin Ithe cutter headiand support lugthe cuttem-sleeye; It'iis only-necessaryflto increase ithe isize of this springwhen the tracertoother machine tools and is not to berestricted' except insofar as isnee'es sitate'd by the priorart and. by the spirit or scope of, the following claims.

' 12"Mechanism*tor'moving a tracer in unison with *the'ilongitudinal movement of a cutter spindle; sleeve (comprising: a cutter spindle sleeve mountedlforlongitudinal movement, a'guidehaving; a. ""fi'xd meniber "having "oppositely :facing spaced; ball-receiving ways, a. relatively movable member" having; ball-receiving ways positioned adjacent 'tjousaid" first=mentioned ways, and .a plurality ofballs"coactingl'with'each set-of ways to: constrain? said. movablesmember. to "reciprocal movementlalong? a 'lineparallefto the path of the?longitudinal'tmovement ofthe cutter spindle sleeve "antii'to-"prevent' said relatively movable meniber"fromi'canting-with' respect to saidfixed member and-thereby m eatingia binding' a'ctlon betweensaiwmenibers whenforce: is appli-ed' to fif said mavfihie -meniher througltan eittending arm;-

an arm rigidly secured to saidrelatlvely movable member and connected with said sleeve whereby the longitudinal movement of -:-said sleeve is directly imparted to said relatively movable mem ber; another arm rigidly secured to said. relatively movable member and arrangedoppositely or said first arm;- and means for mounting a tracer on the end of said second arm;

2. Mechanism for moving a tracer in unison with the longitudinal movement of a cutter spindle sleeve comprising: acutte'r spindle sleeve mounted for. longitudinal movement, a guide having a fixed member having oppositely facing spaced ball-receiving ways,: a relativelymovable memberj having ball-receiving i ways positioned adjacent to said first-mentioned' ways,-:a plurality ofballs coacting with each set of ways -to con* strain said movable member to reciprocal movement along a line parallel to the, path of the longitudinal movement of the cutter spindle sleeve and to prevent said relatively movable member from canting with respect to said fixed member and thereby creating a binding action between said members when force is applied to said movable member throughanextending arm, and a balancing spring to-counter-balance the weight on said movable member; an'arm rigidly secured to said relatively movable member and connected with said sleeve whereby the longitudinal movement of said sleeve is :directl 'imparted to said relatively movable member; another arm rigidly secured to said relatively movable member and arranged oppositely of said first arm; and means for mounting a tracer on the end of said second arm. P

3. In a duplicating machine a cutter head, a cutter spindle-sleeve mounted in said head for reciprocal longitudinal movement, a cutter spindle rotatably mounted in said sleeve, anarm rigidly mounted on and projecting .from 'said cutter head, a guiding member rigidly carried by said arm, a relatively movable member slidably guided by said guiding member for reciprocal motion parallel to the said movement of said sleeve, a control arm rigidly attached to said relatively movable member, interlocking jaw and abutment meansbetween .said sleeve and said control arm'whereby they are caused to move in unison, a tracer-carrying arm detachably secured to said relatively movable member, a tracer carried by said tracer-carrying arm, and compressible means actingbetween'said firstnamed arm and said relativel movable member to-counter-balance said control arm,.-relatively movable member, tracer-carrying -ari n, and tracer. I

4. In a duplicating machine's. cutter head, a cutter spindle sleeve mounted in said h ead for reciprocal longitudinal movement, a' cutter spindle rotatably mounted in said sleeve, an arm rigidly mounted on and projecting from said cutter head, a guiding member rigidly carried by said arm, a relatively movable member slidably guided by said guiding member for'reciprocal motion parallel to the said movement of-said sleeve,v a control arm rigidly attached to said relatively movable member, interlockin jaw and abutment means betweensaid sleevev and said control arm whereby they are caused to move in unison, a tracerrcarrying arm detachably secured to said relatively movablemember, r'xiicr ometer universal adjusting means mounted on said tracer-carrying arm, a tracer carriedby said adjusting-means, and spring means acting. between said rigid mounted arm and said relatively movable member to counter-balance said control arm, relatively movable member, tracer-carrying arm, adjusting means, and tracer.

5. In a machine having a cutter head and a vertically movable cutter spindle earring sleeve, a main support fixed to said cutter head and having at its outer end an elongated casing, a vertically movable control arm having an inner end and an outer end provided with an elongated casing, an elongated vertical guide bearing having relatively slidably engaged parts mounted on said casings to permit vertical movement of said control arm and prevent canting of said arm as force is applied at its inner end, means interconnecting the inner end of said control arm and said sleeve to directly transmit vertical movement thercbetween, a counter-balancing spring mounted between said casings to substantially carry the weight of said control arm and a tracer and tracer-carrying arm, a tracer-carrying arm having one end detachably connected to the casing on said control arm, and a tracer mounted in the other end of said tracer-carrying arm.

6. In a machine having a cutter head and a vertically movable cutter spindle carrying sleeve, a main support fixed to said cutter head and having at its outer end an elongated casing, a vertically movable control arm having an inner end and an outer end provided with elongated casing, an elongated vertical guide bearing having relatively slidably engaged parts mounted on said casings to permit vertical movement of said control arm and prevent canting of said arm as force is applied at its inner end, means interconnecting the inner end of said control arm and said sleeve to directly transmit vertical movement therebetween, a tracer-carrying arm having one end detachably connected to the casing on said control arm, a tracer mounted in the other end of said tracer-carrying arm, and said control arm and tracer-carrying arm being proportioned so that the center gravity of said arms and tracer is substantially centered at said sliding bearing.

7. In a machine havin a cutter head and a vertically movable cutter spindle carrying sleeve, a main support fixed to said cutter head and having at its outer end an elongated casing, a vertically moveable control arm having an inner end and an outer end provided with elongated,

casing, an elongated vertical guide bearing having relatively slidably engaged parts mounted on said casings to permit'ivertical movement of said control arm and prevent canting of said arm as force is applied at its inner end, means interconnecting the inner end of said control arm and said sleeve to directly transmit vertical move ment therebetween, a counter-balancin spring mounted between said casings to substantially carry the weight of said control arm and a tracer and tracer-carrying arm, a tracer-carrying arm having one end detachably connected to the casing on said control arm, a tracer mounted in the other end of said tracer-carrying arm, and said control arm and tracer-carrying arm being proportioned so that the center gravity of said arms and tracer is substantially centered at said sliding bearing.

8. In a machine having a cutter head, a cutter spindle sleeve mounted for vertical movement insaid head, and a cutter spindle carried in said sleeve, tracer-mounting mechanism comprising a main support fixed to said cutter head and having at its outer end an elongated casing, a vertically movable control arm having an inner end and an outer end provided with an elongated casing, an elongated vertical guide bearing having relatively slidably engaged parts mounted on said casings to permit vertical movement of said control arm and prevent canting of said arm as force is applied at its inner end, interlocking jaw and lug means carried by said sleeve and said inner end to directly transmit vertical movement therebetween, a counter-balancing spring mounted between said casings to substantially carry the weight of said control arm and a tracer and tracer-carrying arm, a tracer-carrying arm having one end detachably connected to the casing on said control arm, a tracer mounted in the other end of said tracer-carrying arm, and said control arm and tracer-carrying arm bein proportioned so that the center gravity of said arms and tracer is substantially centered at said sliding bearing.

PETER M. HENKES. FRED STEINBRECKER.

10 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 960,765 Albee June 7, 1910 1,073,547 Tunes Sept. 16, 1913 1,313,543 Keller Aug. 19, 1919 1,440,184 Stenger Dec. 26, 1922 1,959,178 Sassen May 15, 1934 1,964,319 Gorton et al. June 26, 1934 2,161,709 Henkes June 6, 1939 2,389,653 Turchan et a1 Nov. 27, 1945 FOREIGN PATENTS Number Country Date 636,727 Germany Oct. 14, 1936 

